1. Field of the Invention
The present invention relates to a measured data synchronizing system where a plurality of measuring units, such as measuring instruments and sensors, are connected with data processing units such as computers, and specifically, relates to a measured data synchronizing system and a measured data synchronizing method, which can determine measured data whose synchronization is secured among units without being restricted by the number of units.
2. Description of the Prior Art
If various physical quantities of objects to be measured, such as temperature, voltage, etc., are to be measured using a plurality of units, or if a physical quantity of an object is to be measured in a plurality of places using each unit, or in similar cases, synchronization in measured results among these two or more units must be secured. A measured data synchronizing system can secure synchronization in measured data which are measured by each of two or more units.
FIG. 1 is a drawing showing an example configuration of conventional measured data synchronizing systems. In FIG. 1, the data processing unit PC consists of a computer or the like and comprises general communication circuit 10A. Measuring part 10 is composed of two or more units 11 to 1N (where N is a natural number) which are measuring instruments, sensors and/or the like, and its specific unit 11 is connected to the data processing unit PC with general communication line 100, such as Ethernet (registered trademark), to exchange signals with data processing unit PC. Each two of units 11 to 1N in measuring part 10 are connected with dedicated communication line 200, in which signal waveforms are hard to degrade, to exchange signals with each other.
Further, specific unit 11, which communicates with the data processing unit PC and which is also called the main unit, comprises general communication circuit 10A and dedicated communication circuit 10B. Units 12 to 1N are also called subunits and each comprises dedicated communication circuit 10B.
General communication circuit 10A and dedicated communication circuit 10B extract the desired signals from the input signals or output signals to be output after converting them to signals conforming to each communication protocol via general communication line 100 and dedicated communication line 200 respectively. In addition, dedicated communication circuit 10B inputs or outputs synchronizing signals for securing synchronization among units of 11 to 1N and minimizes delay times when synchronizing signals are transferred.
Operation of the system shown in FIG. 1 will be described below. Data processing unit PC outputs a signal composed of setting conditions for carrying out measurement (such as measuring period, measuring range, etc.), and commands for measurement start and end and the like to measuring part 10. These signals are converted to signals for communication (a packet that is a block of data) in general communication circuit 10A in the data processing unit PC and then output to general communication line 100. Main unit 11 in measuring part 10 receives the packet from the data processing unit PC via general communication line 100 as an input, extracts desired signals (setting conditions and commands) with its general communication circuit 10A from this input packet, and carries out measurement or the like based on this extracted signal.
Main unit 11 further converts the extracted signal into a signal having a dedicated communication protocol and outputs this signal to subunits 12 to 1N. Subunits 12 to 1N extract desired signals in each dedicated communication circuit 10B from a packet input via dedicated communication line 200 and start measurement or the like based on these extracted signals.
Further, main unit 11 distributes a synchronizing signal for securing synchronization in measurement by main unit 11 and subunits 12 to 1N to each of subunits 12 to 1N via dedicated communication circuit 10B and dedicated communication line 200. Each of subunits 12 to 1N measures the object to be measured based on the synchronizing signal from main unit 11 to acquire measured data. Measured data acquired by each of subunits 12 to 1N are output to main unit 11 via dedicated communication circuit 10B and dedicated communication line 200.
As described above, measured data which are synchronized among subunits 12 to 1N are input to main unit 11. Main unit 11 outputs the measured data synchronized among subunits 12 to 1N to the data processing unit PC via general communication circuit 10A and general communication line 100.
The data processing unit PC extracts a desired signal, such as measured data, from a packet in general communication circuit 10A, carries out desired processing or analysis of these measured data, and stores the measured data and the results of processing and analysis to a memorizing part not shown in the drawing, such as hard disk and memory, or displays the measured data and the results of processing and analysis in a display not shown in the drawing.
As seen above, it is required to supply a synchronizing signal from main unit 11 to each of subunits 12 to 1N to secure synchronization of measured data in each of units 11 to 1N. It is also required for each of units 11 to 1N to provide dedicated communication circuit 10B respectively in which processing more complicated than in general communication circuit 10A (such as compensation of delay time in the synchronizing signal due to the length of dedicated communication line 200 or regeneration of degraded waveforms) is necessary to synchronize the measured data. Furthermore, dedicated communication line 200 is more expensive than general communication line 100 because the former must transfer the synchronizing signal exactly.
In addition, even if dedicated communication circuit 10B and dedicated communication line 200 are used, increasing the length of dedicated communication line 200 due to the increase of the number of units 11 to 1N degrades the synchronizing signal waveforms, increases the delay time, and causes very large deviation of synchronization between units 11 to 1N. This restricts the number of connectable units 11 to 1N. Although a circuit for further decreasing the delay time for the purpose of securing synchronization can be designed, such a circuit configuration may be more complicated and thus it is not realistic.
On the other hand, for measurement at long intervals over a long time, such as for measurement of data in a plant, it is desired that exact synchronization among units is not required but increasing the number of units is required if synchronization to a certain extent can be secured.
The objective of the present invention is to achieve a measured data synchronizing system and a measured data synchronizing method which can determine the measured data whose synchronization is secured among measuring units without being restricted by the number of measuring units.